1. Field of the Invention
This invention relates to an ultrasonic transducer for use in diagnostic imaging.
2. Description of the Related Art
The importance of diagnostic ultrasound imaging is widely recognized, and has grown as imaging resolution and the range of available uses and features have steadily increased. Once an expensive luxury available only in the best-equipped hospitals, diagnostic ultrasound imaging is now a commonly and almost routinely offered procedure even in some individual physician's offices. Perhaps more importantly, some ultrasound imaging systems are now portable and inexpensive enough to have even in small offices, or in places such as in developing countries with relatively small budgets for such diagnostic tools.
The quality of an ultrasound image is directly affected by many factors and in particular by the properties of the transducer used to generate the necessary pattern of ultrasonic signals and to receive their echo returns. Accordingly, work is constantly in progress to improve almost every major component of a transducer, the materials used in it, and the methods of manufacturing it. During the past 30 years or so, just a few of the large number of improvements include better active materials, triple matching layers, better kerf filling, low-attenuation lens materials, heat treatments and heat sinks, and flex circuit interconnects.
Typically, piezoelectric elements within a transducer are formed as an array and are selectively activated electrically to produce a desired scan pattern. The same array is then switched to receive the return signals, which are then converted back into electrical signals that are processed using known methods. Individual and separate control of elements presumes, however, separate electrical leads in the form of wires, or traces on a circuit board, either printed (PCB) or flexible (flex circuit).
This reality leads to several challenges and trade-offs relating to such issues as, among many others, cross-talk, impedance, physical robustness, heat, integrity and ease of bonding, manufacturing cost and complexity, and even comfort in use. For example, strong lead wires may provide physical robustness, but they may also cause the transducer cable to be so bulky and stiff that it is cumbersome for an operator to maneuver over the body of a patient. However, fine wires or traces that allow for a light, flexible cable are more prone to breaking. As another example, certain transducer structures may be specially designed to be manufactured with certain materials, such as in a backing layer, but may then be difficult to adapt to new materials without difficult and costly changes in the structure and manufacturing procedures.
Many different transducer structures and cabling (including single, double, and multi-layer flex circuits) and interconnect arrangements have, accordingly, been proposed in different contexts involving diagnostic ultrasound imaging. The following U.S. patents, for example, represent proposed solutions to some of the many problems involved in different contexts of diagnostic ultrasound imaging transducers:
U.S. Pat. No. 5,559,388 (Lorraine, et al., “High density interconnect for an ultrasonic phased array and method for making”);
U.S. Pat. No. 5,722,137 (Lorraine, et al., “Method for making a high density interconnect for an ultrasonic phased array”);
U.S. Pat. No. 5,567,657 (Wojnarowski, et al., “Fabrication and structures of two-sided molded circuit modules with flexible interconnect layers”);
U.S. Pat. No. 5,617,865 (Palczewska, et al., “Multi-dimensional ultrasonic array interconnect”)
U.S. Pat. No. 5,920,972 (Palczewska, et al., “Interconnection method for a multilayer transducer array”);
U.S. Pat. No. 6,994,674 (Sheljaskow, et al., “Multi-dimensional transducer arrays and method of manufacture”);
U.S. Pat. No. 5,703,400 (Wojnarowski, et al., “Fabrication and structures of two-sided molded circuit modules with flexible interconnect layers”);
U.S. Pat. No. 5,923,115 (Mohr, III, et al., “Low mass in the acoustic path flexible circuit interconnect and method of manufacture thereof”);
U.S. Pat. No. 6,541,896 (Piel, Jr., et al., “Method for manufacturing combined acoustic backing and interconnect module for ultrasonic array”);
U.S. Pat. No. 6,580,034 (Daane, et al., “Flexible interconnect cable with ribbonized ends”); U.S. Pat. No. 6,651,318 (Buck, et al., “Method of manufacturing flexible interconnect cable”);
U.S. Pat. No. 6,734,362 (Buck, et al., “Flexible high-impedance interconnect cable having unshielded wires”); and
U.S. Pat. No. 7,229,292 (Haider, et al., “Interconnect structure for transducer assembly”).
There is nonetheless always room for improvement, not only in general, but also in the specific context of providing a transducer that is suitable for use beyond the well-controlled world of a diagnostic unit in a large-budget hospital. For example, a transducer for use in the field, or for wide-scale use in developing countries, should ideally be relatively easy to build and the component costs should be relatively low (to allow for greater numbers for a given budget); the performance should be as little limited or reduced as possible; it should be easy to adapt the transducer and its manufacturing process to take advantage of any newly developed materials, or to design changes such as in the number of matching layers. The transducer should also be physically robust and should preferably be more thermally tolerant than conventional probes. This invention at least partially meets one or more of these needs.